Memory devices in the form of integrated circuit (IC) chips are typically provided as internal storage units in a computing or communication device. In general, memory devices contain an array of memory cells arranged in rows and columns for storing data, and row and column decoder circuits coupled to the array of memory cells for accessing the array of memory cells in response to an external address. Each column of memory cells in the memory devices can be coupled to one or more I/O bit lines each for read/write of data from a memory cell designated by the external address.
One type of memory chips used in the computing or communication devices is random-access memory (RAM), such as dynamic random-access memory (DRAM) that stores each bit of data in a separate capacitor within the memory chip, and static random-access memory (SRAM) that uses latching circuitry to store each bit of data. Both types of memory chips are volatile, meaning that content of the memory chips will be lost when the memory chips are not powered. Another type of memory chips used in the computing or communication devices is flash memory, which is an electronic non-volatile computer storage device that can be electrically erased and reprogrammed and can retain stored information even when the memory chips are not powered.
Since memory cells are more prone to defects than other IC chips used in the computing device, one or more columns of redundant memory cells are often included as a part of a memory chip for replacing any defective column and/or its elements (e.g., bit lines, etc.) so that a read/write operation can be performed properly on the memory chip after the memory repair/replacement with the redundant memory columns.